In the tissue manufacturing process, the paper sheet is dried by means of a steam heated drying cylinder, termed a Yankee. Adhesive materials are used to coat the Yankee surface in order to adhere the wet sheet to the dryer. This improves heat transfer, allowing more efficient drying of the sheet, and most importantly provides the required adhesion to give good creping of the dry sheet. Creping is the process of impacting the sheet into a metal blade, thus compressing the sheet in the machine direction, creating a folded sheet structure. Creping breaks a large number of fiber-to-fiber bonds in the sheet, imparting the qualities of bulk, stretch, absorbency, and softness which are characteristic of tissue. The amount of adhesion provided by the coating adhesive plays a significant role in the development of these tissue properties.
The Yankee coating also serves the purpose of protecting the Yankee and creping blade surfaces from excessive wear. In this role, the coating agents provide improved runability of the tissue machine. As creping blades wear, they must be replaced with new ones. This replacement process represents a significant source of tissue machine downtime, or lost production, as creped product cannot be produced when the blade is being changed. Also a problem, especially with the poly(aminoamide)-epichlorohydrin type creping adhesives is the phenomenon of coating buildup. Resins of this type are described in U.S. Pat. Nos. 2,926,116 and 3,058,873 the disclosure of which are incorporated herein by reference. This problem is evidenced by high spots in the coating, which cause chattering, or bouncing of the crepe blade, against the coated Yankee surface. Blade chatter results in portions of the sheet traveling underneath the crepe blade, causing picks or holes in the sheet. This can lead to sheet breaks and machine downtime.
It is the object of this invention to disclose creping adhesive compositions which provide both improved adhesion and improved machine runability over other adhesive compositions known in the art.